(a) Field of the Invention
The present invention relates to a display device.
(b) Description of the Related Art
Recently, flat panel displays such as an organic light emitting display device (OLED), a plasma display device (PDP), or a liquid crystal display (LCD), each of which can be substituted for heavy and large cathode ray tube (CRT) displays, have been actively developed.
The PDP is a device for displaying characters and images by using light emitted by a plasma generated in a gas by an electric discharge, and the OLED is a device for displaying characters and images by using light generated by field emission of particular organic materials or polymers. The LCD is a device for displaying characters and images by using light transmitted through a liquid crystal layer interposed between two panels. The transmittance of light that passes through the liquid crystal layer and a polarizer is controlled by an electrical field applied across the liquid crystal layer.
Flat panel displays, the LCD and the OLED, for example, include a display panel on which a matrix of pixels is provided, each pixel having an associated switching element. Display signal lines, including gate lines and data lines are provided on the display panel. A gate driver is provided for transmitting gate signals on the gate lines to the control terminals of the pixel switching elements. A gray voltage generator is provided for generating a plurality of gray voltages, and a data driver is provided for selecting data voltages, corresponding to video data, from among the gray voltages and transmitting the selected data voltages on the data lines to the input terminals of the pixel switching elements. A signal controller is provided for controlling the gray voltage generator, the gate driver and the data driver.
A small display device, for example, a display device for a cellular phone, includes a display panel, a flexible printed circuit film FPC having wiring for transmitting an external signal, and an integrated circuit chip which functions as a driving chip or a control chip for controlling the display panel and the FPC.
The driving chip generates control signals and driving signals for controlling the display panel, and is usually mounted on the display panel in a form known as chip on glass (COG).
When, in the process of manufacturing a display device, the display signal lines become disconnected or short-circuited, or the pixels become defective, the disconnected and short-circuited display signal lines and the defective pixels can be detected via a number tests conducted during or after the manufacturing process. Such tests include an array test, an in process visual inspection test, a gross test, and a module test, the latter being performed after a driving chip is mounted on the display panel. In the visual inspection test, test voltages are applied to display signal lines and the response or lack of response of pixels is observed.
In the case of a small display device that includes a display panel and a printed circuit film FPC, the display panel and the FPC both include signal lines and pads for transmitting signals, and defective signals lines and defective pads are detected at each test process.
However, only some of the pads can be tested in the visual inspection test, and the rest of the pads cannot be tested until the final module test process is performed after mounting a driving chip on the display panel. Accordingly, a defective pad may not be detected until the final module test process is performed, thereby increasing manufacturing time per acceptable display panel and reducing production yield.